Electrical fencing equipment



Dec. 23, 1958 H. MULLER 2,866,107

ELECTRICAL FENCING EQUIPMENT Filed Sept. 5, 1956 Z SheetS-Sheet 1 INVENTOB Heanz MIJUEP GL IMLW ATTOKN E 85 Dec. 23, 1958 H. MULLER 2,866,107

ELECTRICAL FENCING EQUIPMENT Filed Sept. 5, 195a I 2 Sheets-Sheet 2 INVENTOR Heinz NzH/er BY @I m ATTOILNESS United; States Patent 2,866,107 ELECTRICAL FENCING EQUIPMENT Heinz Miiller, Korbaeh, Waldeck, Germany Application September 5, 1956, Serial No. 608,103

6 Qlaims. (Cl. 307-132) This invention is concerned with electrical fencing equipment for pasturage, of the kind in which electrical impulses are applied to the fence at regular short time intervals by a high voltage transformer 'whose primary winding is energised under the control of a relay during each such time interval by the discharging of a condenser which is charged from a battery or other source of current with simultaneous energisation of the relay. The invention relates particularly to a construction of relay for such equipment. A further feature of the invention relates to a structural combination of such relay with the high voltage transformer.

Although the use of a relay for electrical fencing equipment is very simple and has been known for a long time, it has been little used in practice, especially in the case when a battery is employed as the source of current. Hitherto, in practice, in such equipment, it has been more usual to employ a mechanical pendulum, instead of a relay, for controlling the periodic energisation and deenergisation of the transformer primary winding.

The reason for this is that a pendulum arrangement is better suited to fulfil the very onerous requirements imposed on the controlling contacts, than the constructions of relay hitherto employed, such relay constructions having proved to be unreliable for the purpose. Reliability is however of great importance in pasturage fencing equipment, since such equipment must in practice operate almost without supervision. Failure of the equipment leaves the fence without current and it then ceases to be an effective fence, for a cow can readily and easily break through such a fence, when not energised, and cause serious damage to neighbouring fields.

With pendulum-operated interrupter contacts, as contrasted with relay contacts, comparatively high contact pressures and long contact paths are available for the contacts. Variation of shape-of the contacts due to contact deformation is therefore less likely to lead to operational faults, than in relay equipment, where variation of shape of the contacts can easily cause short-circuiting.

Nevertheless, other causes, such as hearing friction, can give rise to faults in pendulum-operated equipment. Relay-operated equipment, wherein the above-mentioned difiiculties can be satisfactorily overcome, is much to be preferred.

In known relay-operated equipment, what are sometimes known as round type relays (in German "Rundrelais) have usually been employed. Such a relay has a U-shaped iron core, with the relay winding on one limb and the contact spring system on the other limb. The latter limb is provided with a knife-edge act ing as a pivot for the bent relay armature. When the relay winding is energied, the armature swings about the knife-edge and moves an insulating pin carried by the movable spring contact. Problems of friction arise both at the armature pivot and between the armature and the insulating pin. In operation, the armature is attracted owing to the charging current of the condenser, and is released when such charging current falls to a value less 2,866,107 Patented Dec. 23, 1958 time period r of the return stroke, the armature is attracted and the contacts are opened to cut out the transformer primary winding. 'By oscillographic observation of the armature movement (using a smallcoil: fixed to the armature and moving therewith in a magnetic. field) it can be seen that the armature after being set in'movement at the end of the timeperiod t suffers loss of speed while raising the contact owing to thework required for effecting opening of the contacts, so that in fact the speed of contact opening is low. "This speed reduction is unsatisfactory since contact migration ;has time to develop. Improved results can be obtained by soadjusting the armature and contacts that the armature can swing freely before engaging the insulatingrpin of the contact, and can thus develop speed and kinetic energy to increase the speed of contact opening. Even so, however, the arrangement is unreliable, sincethe 1 great frequency of switching operations causefrictional .troubles todevelop during operation which-interfere with the free swinging of the armature and make thecontact operation irregular and slow. It can even happen. that friction at the knife edge can liberate iron dust which can settle between the-armature and'the relay core and ultimatelylead to permanent magnetisation of the'core and therefore .fail

.the armature gives rise to frictional troubles and faults similar to those above described develop at the contacts.

Moreover, the pivotal bearing is very susceptible to damage in transport.

The present invention has for an object to-provide an improved relay construction which avoids the above de- F scribed difiiculties of the known relays and Willoperate with great reliability in electricfencing equipment.

A further object of the invention is to simplify the electric fencing equipment by structurally combining together the relay and the high voltage transformerf Further objects of the invention will be apparent-during the course of the following specification.

To this end according to the invention, the relay comprises a core of magnetic material, at least one relay winding linked with the core, normally clo-sedcooperating contacts, a pair of contact springs respectively carrying the contacts, and an armature which iscarried by, one of the contact springs and acts to open the contacts when attracted by the core. The characteristics of the contact springs are so dimensioned in relation to the mass of the armature that on closing of thecontacts after release of the armature, the resilienceof-the second contact spring causes the armature to swing back with acceleration towards the core. Further acceleration is imparted to the armature by the attraction of the core, whereby the speed of the armature progressively increases up to and past the point .ofseparationof the contacts to its fully attracted position.

The dimensicningiof the spring characteristics and of the. sp ng P UR be e n the contacts is preferably. such that during the opening movement the contacts remain close-d for a long path length and thereby cause the armature to attain at the moment of contact opening, suffi cient speed to prevent appreciable contact arcing or contact migration.

A fuller understanding of the present invention may be had by referring to the following description taken in conjunction with the accompanying drawings, showing by way of example a preferred embodiment of the inventive idea.

Figure 1 shows diagrammatically and by way of example a preferred practical construction of relay according to the invention, and

Figure 2 similarly shows a practical construction of combined relay and transformer.

Figure 3 is a circuit diagram.

Figure 4 shows a Somewhat differently constructed relay.

In the construction of Figure 1, the relay comprises an iron core 1 having an airgap 2 and a relay winding 3, two contact springs 4 and 5 respectively carrying at their free ends cooperating relay contacts 7 and 6, and an armature 8 carried near the free end of the contact spring 4;. The two contact springs 4 and 5 separated from each other by insulating pieces 9 and 10 are secured near one end of the core 1 by means of a holding screw 11. The arrangement is such that in the normal rest position of the contact springs 4 and 5, the contacts 6 and 7 are in engagement with one another. The armature 8 lies adjacent to two poles of the core 1 separated from each other and disposed opposite the air gap 2, so that when the relay winding 3 is energised the arma ture will be attracted to bridge the air gap and to open the relay contacts 6, 7. The attraction of the armature 8 by the core poles imparts energy to the armature, so that in the fully attracted position it has mechanical potential energy E=f P.ds, Where P is the instantaneous restoring force of the contact spring 4 and s is the distance moved by the armature from its normal position, S being the total distance from such normal position to the attracted position. On release of the armature, this potential energy E is is transformed into kinetic energy which reaches its maximum when the contact 7 engages the contact 6 and causes the two contacts to move further away from the core, stressing both springs so that on completion of their forward swing they immediately swing back together, thus initiating the return movement of the armature 8. The characteristics of the springs 4, 5 and the mass of the armature 8 have such dimensions that during the time t the armature goes through about half its return swing and has thus been accelerated to r the maximum value of the speed due to the mechanical spring force, such speed however now being further accelerated by the increasing magnetic force due to the attraction of the magnetic core. Thus, in contrast with the known relays, the kinetic energy acquired by the armature during the releasing movement is itself utilised to ensure a high opening speed for the contacts. The utilisation of this energy moreover enables the stroke of the armature to be increased as also the length of the path of the contacts in their closed position, thus still further increasing the contact opening speed. Thus, the armature may have a stroke of the order of 2 to 3 millimetres, the contacts being in engagement over a distance of 1.5 to 2.5 millimetres. The time t during which the relay contacts should remain in engagement, depends on the electrical constants of the fencing equipment, in which the relay is used, for example L times C, where L is the inductance of the transformer primary winding and C the capacitance of the condenser. The half natural period of oscillation of the swinging spring assembly 4, 5 or 4, 5, 19 respectively, including armature 8 is arranged to be approximately in resonance with this time t but exact agreement is not necessary since, during the time t a steadily increasing magnetic force is being generated which must be added to the spring force in the same direction and in phase therewith.

It is also advantageous, in dimensioning the spring characteristics and the mass of the armature, to choose such mass large enough for it to have acquired at the moment of contact separation a kinetic energy which is not appreciably reduced by the work done in separating the confacts.

The high speed of contact opening is also of advantage in respect of contact migration. Contact materials are known, for example a gold-nickel alloy, which has very small contact migration and contact voltage in the order of 10 volts or less. When the relay con tacts open the contact voltage increases since cutting out Of the inductance of the transformer primary winding, generally in accordance with a sine wave from zero to a peak value which can reach volts or more. In the relay according to the invention, the contact opening speed can be made so great that the contacts are widely separated when the contact voltage has increased only to about 10 volts, thus enabling such contact materials to be used with full advantage.

In practice, the relay can be arranged to operate at a frequency of one operation per second. The armature after release at each operation is attracted again in a small fraction of a second, for example between 20 and 40 milliseconds as the primary winding of the transformer is switched in and out again within this very short period.

It is to be noted that in the relay according to the invention, the difficulties arising in the previously known relays from friction at the armature pivot and also between the armature and the insulating pin on the contact spring, are completely eliminated. The relay can therefore continue to operate with its favourable conditions as regards avoidance of contact migration, notwithstanding the frequent repetition of contact operation. The elimination of armature friction also avoids risk of the formation of iron dust.

In relay-controlled fencing equipment operated by rectified mains voltage instead of battery voltage, the problem of contact migration is not of serious significance. In such equipment the relay cuts out the transformer primary winding at a moment when the high frequency condenser discharging current has become practically Zero. The elimination of armature friction, however, in the relay according to the invention makes such relay much more reliable than prior known relays, even in equipment operated by rectified mains voltage.

In the construction of Figure 2, wherein the same reference numerals have been used as in Figure 1 with the same significance, the iron core 1 which carries the relay winding 3 is formed in one piece with the iron core 1a of the associated high voltage transformer. The limb 1 4 of the composite core is common to the magnetic circuit of the relay winding 3 and to that of the transformer, whose primary and secondary windings are shown respectively at 12 and 13. This combined relay and transformer construction operates in the manner already described with reference to Figure 1, but has the added advantage of affording a very desirable economy in space in the pasturage fencing equipment. The composite core, 1, 1a is preferably made in the usual way from a stack of stamped laminae, although it would be possible, with the known disadvantages, to make such core of solid metal, if desired. The combined construction of Figure 2 affords an advantageous simplification in comparison with the known relays of the round type and of the fiat type, wherein the relay core must necessarily be independent of the transformer core.

It is to be understood that'the'particular constructions described have been given by way of example only and can be modified in various ways within the scope of the invention. For instance, further contacts operated by the diagram of one simple arrangement of electrical fencing equipment incorporating the relay above described, the same reference numerals as in Figures 1 and 2 again beng employed. This diagram shows the relay 3, 6, 7, 8 in appropriate circuit relationship with the high voltage transformer 12, 13 and the condenser 15, energised from a source 16, the fence itself energised from the transformer secondary 13, being indicated at 17. A condenser 18 is arranged in parallel to the contacts 6 and 7 so as to extinguish sparks between the said contacts.

As will be obvious to those skilled in the art the expression hereinbefore employed and employed in the claims that the armature (3) is carried by one of the contact springs (4 or 5) is to be understood in a broad sense to include, for example, a modified arrangement in which the armature is carried by a spring separate from that carrying the associated contact, such contact and the armature being so coupled that the contact and the armature will move together when the armature is attracted to the core on energization of the relay winding.

Such modified arrangement has been diagrammatically shown in Fig. 4 of the accompanying drawings, the same reference numerals as in Figs. 1 to 3 being employed. Thus, Fig, 4 shows the core 1, the airgap 2, the relay winding 3, the contact springs 4 and 5, the contacts 6 and 7, the armature 8, the insulating pieces 9 and 10, and the holding screw 11. Here, however, the armature is carried by a separate spring 19. The contact spring 4 and the spring 19 or its associated armature 8 are coupled by a coupling means, e. g. a hook 20, so as to swing together, when the relay winding 3 will be energized and will attract the armature 8.

The characteristics of the spring assembly comprising the springs 4 and 5, 19, are so dimensioned in relation to the mass of the armature that on closing of the contacts after release of the armature the resilience of the spring assembly causes the armature to swing back with acceleration towards the core, further acceleration being imparted to the armature by the attraction of the core, whereby the speed of the armature progressively increases up to and past the point of separation of the contacts to its fully attracted position.

What I claim as my invention and desire to secure by Letters Patent is:

1. Electrical fencing equipment of the kind in which electrical impulses are applied to a fence at regular time intervals in the order of one second, said equipment comprising a condenser, a source of direct current connected with said condenser for charging said condenser, a high voltage transformer comprising a primary winding having one end connected with said source and another end connected with said condenser, and a secondary winding having one end connected to the fence, and a control relay having a core of magnetic material and comprising two normally closed cooperating contacts, one of said contacts being connected with the primary winding of said transformer and the other contact being connected with said condenser, an armature, a spring assembly comprising means carrying and operating said contacts and a spring carrying said armature, said spring body located in a normal intermediate position when the relay is deenergized; said armature being located in the magnetic field of said core, at least one relay winding cooperating with said core and having one end connected with said source and another end connected with said condenser and said contacts, whereby said armature is attracted by said core to move said spring carrying said armature away from said normal intermediate position when the relay winding is energized by the charging current of said condenser and whereby said spring is kept away from said normal position and said contacts are kept separate during said regular time interval as long as said charging current continues and whereby said spring and its armature are then released from said core; said spring assembly and being swingable in its entirety away from said core and from said normal position to a point of reversion and back to said normal position and so as to close said contacts during said one forward and backward swing and during a predetermined relatively short contact closing time interval, each of which short time intervals beginning at a time when the assembly is substantially in said normal position and ending at another time when the assembly is again close to said normal position whereby said primary winding of the transformer is energized for said short time interval through said contacts by the discharging of said condenser and whereby simultaneously a charging current of said condenser flowing from said source through said relay winding is generated which again pro duces a field re-attracting said armature and separating said contacts when said primary winding has been energized by said discharging current to a substantial degree thus producing one of said electrical impulses in said secondary winding; said spring assembly together with said armature having resilient, natural frequency and mass characteristics so predetermined as to give said backward swinging at the second-mentioned time and past said normal position the same phase and direction as those of the magnetic force of said last-mentioned field re-attracting said armature, whereby said backward swinging accelerates said contact separating effect of said magnetic force.

2. An electrical fencing equipment in accordance with claim 1, wherein said high voltage transformer is a core of magnetic material constituting a single integral unit with the core of the relay.

3. Electrical fencing equipment in accordance with claim 1, wherein said spring assembly comprises a pair of contact springs respectively carrying the cooperating contacts, a third spring carrying the armature, and coupling means between such springs, whereby one of the contact springs and the third spring are caused to move together when the armature is attracted by the core.

4. Electrical fencing equipment in accordance with claim 1, wherein said spring assembly comprises a spring carrying one of the cooperating contacts and a second spring carrying both the other contact and the armature.

5. Electrical fencing equipment in accordance with claim 1, wherein said armature consists of a mass which is sufficient to insure that its kinetic energy at the moment of contact opening is large in comparison with the work to be done in opening the contacts and that the energy is maintained after contact opening.

6. Electrical fencing equipment in accordance with claim 1, wherein said cooperating contacts consist of a goldnickel alloy.

References Cited in the file of this patent UNITED STATES PATENTS 2,510,337 Franklin June 6, 1950 2,560,056 Westin July 10, 1951 2,617,950 Lace Nov. 11, 1952 

